The goal of this project is to determine how a eukaryotic gene is organized and expressed in a tissue-specific manner. To achieve this goal, this application proposes a thorough molecular and genetic analysis of the maize P gene, which controls the pigmentation of specific floral organs. The pigmentation is non- vital, so mutants are readily isolated and studied; molecular probes for the P locus are available; and transposable elements associated with P can be harnessed as in vivo probes of gene structure and regulation. Together, these features make P uniquely suited for analyzing developmental gene regulation. In preliminary studies, the transposable element Ac was used as a probe to isolate a DNA clone from the P locus. The P clone was then used to detect putative P transcripts, and to determine the structures of mutant P alleles. In the work proposed here, the precise exon/intron structure of the P gene will be determined by isolating and sequencing cDNA clones. Northern blotting will elucidate the pattern of P RNA expression as a function of tissue and developmental stage. The molecular studies will be complemented by a genetic program designed to efficiently saturate the P locus with Ac insertions. The site of Ac insertion in each mutant allele will be determined and correlated with the mutant phenotype to produce a functional map of the P locus. Results obtained will also elucidate important determinants of transposition: direction, distance, and sequence specificity. Further, transposable element-induced genetic chimeras will be examined to reveal cell lineage relationships in maize floral development. Additional experiments will critically examine the possibility of developmental control of gene action by transposable elements. The results of this study should reveal general mechanisms of gene regulation and development which may contribute significantly to an understanding of human health and disease.